1. Field of the Invention
The present invention relates to a semiconductor with a stabilizing capacity in which a plurality of integrated individual function blocks are arranged and in which a power supply unit capable of controlling an arbitrary individual function block in a standby state.
2. Description of the Related Art
In recent years, a semiconductor integrated circuit (hereinafter referred to as LSI) has been made in a finer process and thus in order to keep a dielectric strength and reliability of transistors, a power supply voltage to be applied is made lower. Moreover, there has been a trend to make a sub-threshold current passing through the transistors larger. In a case of constituting an inexpensive system, however, there are many cases where a power supply voltage of a device other than an LSI can not be made lower and thus a voltage drop circuit is built in the LSI. Because the voltage drop circuit needs a load capacity for stabilizing voltage and it is also required to reduce the number of parts and to limit the number of terminals in the system, there has been a tendency to build also the load capacity in the LSI and thus, even if the LSI is made in the finer process, an effect of downsizing the area of the LSI becomes smaller.
Moreover, while a need for the LSI used in a battery-driven type portable electronic device to decrease power consumption in a standby state has increased, the voltage drop circuit must have a comparator in itself and thus the power consumption of the voltage drop circuit itself becomes large, then the LSI in which the voltage drop circuit is built, presents a technical problem of reducing power consumption in the standby state.
Technologies for reducing the power consumption of the LSI include a technology disclosed in Laid open Japanese Patent Publication Hei 06-232349 titled “SEMICONDUCTOR INTEGRATED CIRCUIT” (literature 1). According to this technology, a power supply voltage Vcc of an unused function block is switched to a base voltage Vss in a power switching circuit to bring the function block into a non-active state to thereby reduce power consumption. Moreover, one of the technologies for reducing the power consumption of the LSI in which the voltage drop circuit is built is disclosed in Laid open Japanese Patent Publication No. 2002-49443, titled “INSIDE VOLTAGE REDUCTION CONTROL SYSTEM” (literature 2). According to this technology, the voltage drop circuit is provided in each function block and voltage is reduced in each function block, whereby the power consumption of the whole LSI is reduced.
The semiconductor integrated circuit in the prior art is constituted in the manner described above and thus presents the following problems. In a case where the technology disclosed in the literature 1 is applied to the LSI in which the voltage drop circuit is built, when a power supply of the function block is switched to a base voltage Vss (earth potential) in the standby state, because a gate parasitic capacity of the function block becomes null, a stabilizing capacity of the voltage drop circuit needs to be a large value, which results in increasing a surface area of the LSI in advance. Moreover, since the technology disclosed in the literature 2 has the voltage drop circuit for each function block, the technology not only has a disadvantage in area but also increases the total amount of power consumed in the respective function blocks.